Target heart rate?

So, as everyone knows by now, I'm the worst possible martial artist when it comes do doing fitness "correctly." I decided to actually research "proper" running and compare it to what I was doing.

Background:
I run 5 miles every other day (except weekends, when I don't exercise because I am the lazyness) and I'm 23 years old.

For the past two weeks I've tracked by heartrate and during my runs (which lasts about 40-50 minutes depending on stuff) my heartrate is about 170. Is keeping my heartrate that high for that long a bad thing?

You'd be better off doing shorter faster runs . Less strain on the joints.

Who, for Pete’s sake! Is opposing science? In fact, we want MORE science by CRITICALLY ANALIZING the evidence-Connie Morris, Kansas State BOE (bolding and underlining part of original quote, red is my emphasis)

As long as you try to treat your subjective experiences as if they were objective experiences, you will continue to be confounded by people who disagree with you.-some guy on an internet messageboard

Not knowing your specific physical condition (i.e cardio vascular or respiratory probelms), it sounds like you are in a good zone if not a touch high to train general cardiorespiratory fitness and the involved slow twitch muscles for endurance according to ACSM guidelines.

If you are interested in training your cardiorespiratory fitness specifically/mainly for martial arts (fights) you may consider changing your program. Fights use high intensity "bursts" of energy followed by a period of active rest. Activities in the duration of ~<1min are support by the ATP-CP and anaerobic glycolysis systems. Fast twitch muscles are responsible for these motor functions (high intesty, short duration). Training your body like you'll use it will have the greatest cross over to your MA. To do this think about interval training (jog-sprint-jog & repeat). There have been specific recommendations laid out in other threads (search: HIIT or interval training).

Some dude took some elite olympic rowers and shackled them to rowing machines to see how high their heart rates could go. He found the theoretical maxes, broke 'em down %-wise and correlated a bunch of metabolic happenstance with the THRs.

I use heartrate mainly for cycling but you should find out your actual max HR. The standard 220 minus age is OK but doesn't always work that well. For instance I'm in my 30's but have a max HR of about 200 when cycling. However this is the max heartrate for cycling. If I'm running I find that I can't get up that high because my body simply can't keep up the pace. Go figure. So you should try to warm up and then do a very hard sprint until you feel like you're about to collapse. Then either quickly look at your watch (if your vision isn't blurry ;) ) or use the MAX HR record feature to see what you got.

The important thing is to not operate in the 80-85% range. This is a zone they say is too fast for endurance training and not hard enough to work the anaerobic system. There is a good debate around this though. I'll generally stay below about 80% for endurance training and go 85-100% for intervals (http://www.cptips.com/hrmntr.htm). I acutally use a wattmeter on my bike now instead of HR. It's more accurate for doing workouts but this isn't practical if you're jogging.

More recently I've ditched the HR monitor and just use perceived effort (http://www.cptips.com/percxtn.htm). This is easier once you get a good idea of how hard you're working. This is where the HR comes in because you can see what your levels of intensity really translate to.

I've used HIIT training before and it does work well. I think for fighting it's great because you frequently have these really fast bursts of speed followed by brief recoveries. It's hard on the knees though jogging when doing the intensity you need. Be careful.